Spintronic devices are being currently developed, wherein spintronic devices harness the spins of electrons (rather than just their electric charges), which may enable new features and functionalities that go beyond those possible with conventional electronic devices. Several spintronic device implementations and applications thereof are carried out in recent times which specifically exploit spin properties instead of or in addition to charge degrees of freedom. The prototype devices that are already manifested vastly in industries span read heads of modern hard-disk drives and memory-storage cells or MRAM (magnetic random access memory), which comprises either giant-magneto resistive (GMR) multi-layered, thin film structure or tunneling magnetoresistive (TMR) thin-film multilayers. A GMR device comprises alternating ferromagnetic and nonmagnetic metal layers. Depending on the relative orientation of the magnetizations in the magnetic layers, the device resistance (also called magneto-resistance) changes from small (parallel magnetizations) to large (antiparallel magnetizations), which may be used to sense changes in magnetic fields. The magnetic tunnel junction (MTJ), on the other hand, comprises two ferromagnetic layers (a fixed/pinned layer and a free layer) separated by a thin insulating layer (typically a few nanometers) (also called the tunneling layer), wherein the tunneling current tunneled through the tunneling layer depends on the relative spin orientation of magnetizations of the two ferromagnetic layers, which can be changed by an applied magnetic field.
Current efforts in designing and manufacturing spintronic devices with magnetic tunnel junction architecture spawn areas such as nano diode or nanometer-scale radio-frequency detector, or nano oscillator which could be used as microwave generating device and microwave detecting device. All these phenomena were based primarily on ‘Spin Momentum Transfer’ (SMT) or ‘Spin Transfer Torque (STT)’.
Nanoscale, spintronic microwave oscillators, which are designed and patented on the Spin-Transfer Torque (STT) effect, commences primarily by passing a dc current through a MTJ. The dc current, gets polarized by the fixed or pinned magnetic layer thereby exerting a STT on the free magnetic layer to drive it into periodic precessional states.
Improvement of the quality factor (i.e. ratio of output frequency and its width) and power output of these nanoscale spintronic oscillator promises better device capability and various work is going towards this end. Thus, an alternative feedback scheme (not based on the spin-transfer torque effect) is of current focus to drive a MTJ device into spontaneous oscillations with higher quality factor.